This invention relates to valves, and in particular to valves having a nut through which is threaded a power-driven rising (and descending) rotating valve stem.
It is known in the prior art to provide torque-sensing means to sense that the valve has become closed and to use such torque-sensing means to shut off the power to the drive motor.
The present invention is directed to the problem which arises because of the inertia or kinetic energy of the drive motor. This problem is particularly troublesome where high-speed motors are used. Inertial forces cause the motor to continue to run after the power has been shut off, and this causes the continuation of application of a closing force on the valve seat after the closure element has been fully seated. Unless prevented, this tends to damage the valve seat.